Generally, using an automatic transmission, the transmission gear is maintained at an optimal position by controlling hydraulic pressure which is set by the speed of the vehicle.
Therefore, the operation of an automatic transmission in a vehicle requires minimum effort on the part of the driver, and removes the necessity for the driver to use a clutch pedal. Also, the automatic transmission makes driving easy since there is little possibility of the engine stalling due to driver error or unskilled operation.
The conventional transmission controls rotary power of the fluid by operating a torque converter in accordance with the output power of an engine, and feeds hydraulic pressure to a corresponding valve according to the control signal applied in a transmission control system.
Hydraulic fluid from an oil pump is pressure regulated by a hydraulic pressure valve and used to control a plurality of parts in accordance with a transmission lever selected by the driver, the speed of the vehicle, and the opening of the throttle. The hydraulic pressure is coupled to friction members through the ports to control the operation of a planetary gear resulting in a drive gear operated at a set transmission ratio. The transmission ratio is fed to a first drive gear which engages a final reduction gear via a second drive gear which, in turn, engages the drive gear.
When the automatic transmission automatically changes speeds, in accordance with the speed of the vehicle, the necessity for reducing the shift shock generated due to the repetitive operation of the friction members occurs. It is possible to minimize the shift shock by controlling the hydraulic pressure for controlling the operation of the front clutch by varying the duty ratio for a hydraulic pressure control solenoid valve according to the respective state of the transmission.
However, the conventional transmission does not control the hydraulic pressure for the purpose of reducing shift shock at the third-to-first speed, skip shift. Therefore, a driver using a conventional transmission in the third-to-first speed skip shift state faces a large shift shock since the operation of the front clutch, which has been operated in third speed is disengaged and thereby the hydraulic pressure, which has been fed to the front clutch, is abruptly exhausted.